Single-part or one-part compounds may cure, set, or harden via a chemical reaction with an external energy source, such as radiation, heat, moisture or the like. Multi-part compounds may cure, set, or harden by mixing one or more component parts which chemically react. This reaction causes polymers to cross-link into acrylics, urethanes, and epoxies.
Polyepoxides, commonly known as epoxy resins or epoxies, are a class of reactive pre-polymers and polymers. As described above, epoxy resins may react with themselves, (e.g., one-part compound), or may react with various co-reactants, commonly referred to as hardeners or curatives, such as phenols, alcohols, and thiols, (e.g., two-part compounds). Reactions of epoxy resins, both with themselves or with a co-reactant, form a thermosetting polymer. Thermosetting polymers are generally characterized as strong, hard materials that are resistant to chemicals and temperature changes. Thermosetting polymers have a wide range of industrial applications, including adhesives, insulators, sealants, coatings, potting/encapsulation, automotive primer, use in electronic and electrical components, or the like.
Single-part or one-part compounds may be dispensed directly from their packaging, (e.g., a tube, a cartridge, or the like), whereas two-part compounds must be pre-mixed. Pre-mixing component parts ensures uniformity in the mixed components prior to a dispensing process. The pre-mixing process may be conducted manually or by an automated device.
A manual pre-mixing process generally requires a user to manually mix both component parts, for example with a mixing spatula and tray. This process is time consuming, results in a high rate of compound consumption, and is attributable to a high incidence of user rotation due to the physical labor required to mix the component parts. In addition, if the user employs a dispensing device, the user generally must load the compound into the dispensing device, which may result in a loss of some compound during a transfer.
Alternatively, an automated device may mix the two component parts and release the resulting compound into a separate compartment, such as a dispensing device, a dispensing syringe, or the like. Two-part compounds, generally characterized by limited working times, (e.g., 20 minutes or less), may begin to cure in the dispensing device and/or related components. This attribute may lead to clogging or inoperability of the dispensing device. This may result in increased maintenance, increased part replacement events, increased cleaning costs, and a high rate of liquid compound waste. One-part compounds may have similar limited working times and deficiencies. This problem may be common to high pressure dispensing valve systems with multiple component parts, such as a spool valve. Such systems are generally self-contained and are difficult to disassemble or are incapable of being disassembled. In such a system, a spool valve may become engulfed by cured compound and prevented from operating properly (e.g., the precision of liquid compound dispensed may vary substantially). Thus, there is a need for a dispensing system and related components that are designed to accommodate the limited working time of one-part and multi-part compounds.
Dispensing systems known in the art employ manual or pneumatically operated dispensing devices. Both manual and pneumatic dispensing devices use a time/pressure system. FIG. 1 is a diagram of a conventional time/pressure dispensing system 100. The time/pressure dispensing system 100 may be pneumatically operated. Referring to FIG. 1, there is shown a pneumatically operated dispensing syringe 105 comprising a plunger 115, and a tip 120. The dispensing syringe is attached to tube 110. Tube 110 may be attached to an air compressor and a vacuum. The compressor applies compressed air at a specific pressure to the plunger 115 to force a volume of a liquid compound 125 within the syringe 105 to be dispensed from the tip 120 onto a surface of a workpiece 130. In this time/pressure system, the higher the pressure and the longer it is applied, the greater the quantity of liquid compound will be dispensed. The vacuum may be used to prevent the liquid compound from dripping. Alternatively, no vacuum may be employed, and the liquid compound held within the syringe may be pulled back from the tip of the syringe due to a depressurization or decrease in the amount of applied pressure.
One of the deficiencies in such a time/pressure system is the inconsistent dispensing quantity caused by internal and external variations. For example, when pressure or force is applied to the liquid compound or a cartridge piston to dispense a quantity of liquid compound, there is a reactionary exertion of force on the piston in the opposite direction. This reaction force may increase when viscosity properties of the liquid compound increase. For example, pulsed pressure may heat the material, which may change the viscosity of the liquid compound and in turn may alter the volume of liquid compound that is dispensed. In addition, the reaction force may decrease as the amount of liquid compound in the dispensing device decreases. The dispensing pressure is generally maintained at a constant level and does not take into account the change in the reaction force, resulting in a high degree of variation in the quantity of liquid compound that is dispensed.
Moreover, additional dispensing parameters may vary as the syringe empties, resulting in variations in the amount of liquid compound dispensed. Vacuum-pull back systems may also be ineffective from preventing liquid compound from dripping and may pull the liquid compound away from the tip resulting in a variation in the volume of the next dispensed amount of liquid compound. Thus, there is a need for a dispensing device and related components that are designed to dispense precise amounts of liquid compound with a high degree of repeatability while taking into account the internal and external variations impacting such as system.